If you are referring to scouting-based observations (e.g. Is player so-in-so taking a different approach at the plate?), comment away. If you are referring to strictly statistical trends, it's simply a matter of how confident you are that the trends you see represent reality. If we want to use a player or team's performance over a period of time to estimate expected future performance, the sample size plays a huge role in knowing how confident we can be in that estimate. Any statistical estimate should really include confidence intervals. Using the simplest example, if I have a special coin that flips heads a constant percentage of the time between 0-100%, we can estimate the true percentage of heads based on flipping that coin. The more times we flip it, the better the average head flip percentage represents the actual percentage. In the baseball world, it's a lot more complicated of course. We have to deal with many other variables and we also have to consider regression to the mean. There are articles that have been written on this topic that explain all this much better than I could but if you want to know how relevant this year's stats are to a players expected future performance, I have a trick for you. For a particular player, just compare his preseason projection to an updated projection (includes his performance so far this year). Fangraphs has the ZiPS preseason projections as well as a rest-of-season (ROS) projection. here's an example: Armis Ramirez: ZiPS preseason: .278/.340/.476 2012: .174/.235/.283 ZiPS ROS: .271/.333/.465 http://www.fangraphs.com/statss.aspx?playerid=1002&position=3B That is not an insignificant difference but it's not exactly predicting a terrible season going forward, either.